BACKGROUND:Developing a model of focal cortical dysplasia in microgyrus and observing the ultrastructure of focal tissue is of important significance for analyzing the pathology of cortical developmental disorder and the factors of structural changes. OBJECTIVE:This study was to observe the pathological characteristics of focal tissue around the microgyrus of rats with cortical developmental disorder using an electron microscope,so as to analyze the causes associated with cerebral cortical developmental disorder. DESIGN:A randomized controlled animal experiment. SETTING:The First Affiliated Hospital of Chongqing Medical University. MATERIALS:This study was carried out in the Chongqing Key Laboratory of Neurology,Room for Electron Microscope of Chongqing Medical University,and Laboratory Animal Center,Research Institute of Surgery,Daping Hospital,Third Military Medical University of Chinese PLA between January 2004 and August 2006.Eighteen healthy newborn male Wistar rats,weighing 3.0 - 6.0 g,provided by the Laboratory Animal Center,Daping Hospital,Third Military Medical University of Chinese PLA,were involved in this study.The protocol was carried out in accordance with animal ethics guidelines for the use and care of animals.Probes (Chongqing Wire & Cable Factory,China) were made of copper core wire with diameter of 1 mm.METHODS:The rats were randomly divided into 3 groups with 6 in each:normal control group,liquid nitrogen injured group and sham-operation group.①In the liquid nitrogen injured group,a blunt probe frozen by liquid nitrogen was placed on fronto-parietal crinial bone of rats for 8 s.A 3 - 5 cm of microgyrus was induced in the unilateral cerebral sensory cortical area.In the sham-operation group,probe was placed at the room temperature.In the normal control group,rats were untouched.② The conscious state and electrical activity of brain of rats in each group were observed.③ 2-3 mm thickness of hippocampal tissue with coronary section was taken for observing its ultrastructure under a transmission electron microscope. MAIN OUTCOME MEASURES:①The ultrastructure of hippocampal tissue.②The conscious state and electrical activity of brain of rats. RESULTS:Eighteen rats were enrolled in the final analysis.① Observation of hippocampal ultrastructure: Electromicroscopic pathological findings showed that for each rat of the liquid nitrogen injured group, mitochondrium in the pyramidal neuron around the microgyrus was swelled,endoplasmic reticulum was expanded,glial cells were swelled,water gathered around the blood capillary,partial medullary sheath was degenerated,neuropilem was normal and no obviously abnormal synapse was found.② Changes in conscious state of rats:Rats in the normal control group and sham-operation group had no convulsive seizure, but those in the liquid nitrogen injured group had occasionally.Most of them showed increased activities, excitation and restlessness,scratching and frequent " watching face-like activities".③Electrical activity of brain of rats:Electroencephalogram recording of liquid nitrogen injured group showed that small wave amplitude of rhythm took the main part.No typical sharp wave,V wave,sharp and slow wave,V and slow waves were discharged. CONCLUSION:Liquid nitrogen can lead to cerebral cortical developmental disorder.Pathological changes of ultrastructure of focal tissue around the microgyrus can provide pathological basis for epilepsy associated with focal cortical developmental disorder.